The present invention relates, in general, to electronic circuits for operating electric motors, and more particularly, to a novel low noise motor drive circuit.
In the past, various forms of electronic circuits had been utilized to drive electric motors. The most efficient motor drive circuits included a pair of power transistors, such as power metal oxide semiconductor field effect transistors (power MOSFETs), that were connected in a stacked configuration between the terminals of a power source for the motor. An output from the stacked transistors was connected to a terminal of the electric motor. Such circuits alternately switched the terminal of the motor between two sides of the power source in order to operate the motor. During the switching of the motor, transient voltages and currents were produced which effected the operation of the transistors and of control circuitry which operated the transistors. Each transistor generally had a freewheeling diode connected in parallel across the transistor to dissipate energy from the motor and to steer the energy back to the power source. As the diode dissipated the energy, it induced noise in the form of perturbations in the current flow from the power source. The noise was coupled to other logic and control circuits which were also connected to the power source, some of which were utilized to sequence switching of the power transistors. The noise often caused improper operation of the logic and control circuits, which often caused improper operation of the motor.
Accordingly, it is desirable to have a low noise motor drive circuit that minimizes the amount of noise induced into the power source.